Overproduction and single-step purification of GAL4 fusion proteins from Escherichia coli.

A DNA fragment encoding the yeast GAL4 transcriptional activator DNA-binding domain (amino acids 1-93) was cloned into an Escherichia coli expression vector such that the overproduced protein is tagged with six histidine residues and a factor Xa protease cleavage site. The vector also contains unique restriction sites at the 3' end of the gene to allow the construction of fusion proteins. These fusion proteins can easily be purified to homogeneity and their activity tested in vitro.